*::after, *::before {
  box-sizing: border-box;
}

*{
  margin: 0;
  padding: 0;
  box-sizing: border-box;
  scroll-behavior: smooth;
} 

:root{
  --clr: #fff;
}

body {
  display: flex;
  flex-flow: row wrap;
  justify-content: center;
  align-items: center;
  height: 100vh;
  background-color: var(--clr);
}

.navigation{
  width: 420px;
  height: 70px;
  background: #209cff;
  display: flex;
  flex-flow: row wrap;
  justify-content: center;
  align-items: center;
  box-shadow: 0 5px 15px rgba(0,0,0,.1);
  border-radius: 10px;
}

.navigation ul {
  position: relative;
  display: flex;
  flex-flow: row wrap;
  width: 350px;
}

.navigation ul li {
  position: relative;
  list-style: none;
  width: 70px;
  height: 70px;
  z-index: 1;
}

.navigation ul li a {
  position: relative;
  display: flex;
  justify-content: center;
  align-items: center;
  width: 100%;
}

.navigation ul li a .icon {
  position: relative;
  display: block;
  font-size: 1.5em;
  color: #FFF;
  line-height: 70px;
  opacity: .75;
  transition: .5s;
}

.navigation ul li.active a .icon {
  opacity: 1;
  color: #209cff;
  transform: translateY(-8px);
}

.indicator{
  position: absolute;
  top: -10px;
  width: 70px;
  height: 70px;
  background: var(--clr);
  border-bottom-left-radius: 35px;
  border-bottom-right-radius: 35px;
  border: 6px solid var(--clr);
  cursor: pointer;
  transition: .5s;
}

.indicator::before {
  content: '';
  position: absolute;
  top: 4px;
  left: -25.75px;
  width: 20px;
  height: 20px;
  background: transparent;
  border-top-right-radius: 16px;
  box-shadow: 4px -6px 0 2px var(--clr);
}

.indicator::after {
  content: '';
  position: absolute;
  top: 4px;
  right: -25.75px;
  width: 20px;
  height: 20px;
  background: transparent;
  border-top-left-radius: 16px;
  box-shadow: -4px -6px 0 2px var(--clr);
}

.indicator span {
  position: absolute;
  bottom: 0px;
  left: -1px;
  width: 60px;
  height: 60px;
  border: 4px solid #209cff;
  border-radius: 50%;
  box-shadow: 0 5px 15px rgba(0,0,0,.15);
  transform: scale(.85);
}

.navigation ul li:nth-child(2).active ~ .indicator {
  transform: translateX(calc(70px * 1));
}

.navigation ul li:nth-child(3).active ~ .indicator {
  transform: translateX(calc(70px * 2));
}

.navigation ul li:nth-child(4).active ~ .indicator {
  transform: translateX(calc(70px * 3));
}

.navigation ul li:nth-child(5).active ~ .indicator {
  transform: translateX(calc(70px * 4));
}